Thin specimens advantage

The origins of analytical electron microscopy go back only about 15 years when the first x-ray spectra were obtained from submicron diameter areas of thin specimens in an electron microscope [1]. Characterization of catalyst materials using AEM is even more recent[2,3] but is currently a very active research area in several industrial and academic laboratories. The primary advantage of this technique for catalyst research is that it is the only technique that can yield chemical and structural information from individual submicron catalyst particles. 

X-ray and electron diffraction techniques have been used to obtain the data on epitaxy. X-ray diffraction methods are particularly useful for thick oxide films and have the advantage of giving diffraction patterns from both the oxide film and the metal suhstrate. For oxide films less than several hundred Angstroms thick, electron diffraction techniques are necessary in most cases, hi general, an electron diffraction pattern is not obtained from the metal substrate unless the oxide film is extremely thin, the surface is only partially covered with oxide, or the metal surface is rough. Reflection type diffraction techniques have been used with bulk specimens and transmission techniques with thin specimens and stripped oxide films from bulk metal specimens. Bach technique has its special advantages and limitations, but these will not be discussed here. 

A recent development (<55) has been the use of much higher voltages, the prime advantage of which is that relatively thick samples may be examined for example, specimens of 2-3 jum are readily studied at voltages of 1000 kV. This means that the severe limitations of having to use thin specimens are obviated. 

Thin sections cut with a diamond knife microtome can be of great advantage in locating regions of catalyst where important chemical or structural changes take place during reaction. Comparison of equivalent areas of fresh and deactivated catalyst can be a difficult problem if the catalyst support does not have a uniform microstructure as in carbon supports produced from plant materials. Even when specimen selection and preparation are adequate, it may be difficult to know upon which image features to place the electron beam to solve the problem at hand. 

Specimens on grids are an alternative to self-supporting disks. Specimens in the form of small particles may be supported on a thin film (e.g. an amorphous carbon film) before being placed on the grid. Thin slices of the material may be produced by an instrument known as an ultramicrotome. The principal advantage of the technique is that it leaves the chemistry unchanged, and it may be employed to create uniform thin films of multiphase material. The instrument operates by moving... 

Therefore, Ca, Cb and pt can be determined simultaneously by measuring X-ray intensities (if the specimen density and thickness are known). Only f factors are required and k factors are not used. This approach can be extended to any multi-component system if one assumes J]Ci=l. The factors are measured from standard thin films with known composition and thickness, the advantage being that pure element thin films can be applied as standards. 

Modern lithography techniques can be used to make many submicrometer windows on the sample. The sample can then be thinned to obtain many small transparent regions. The advantage is that if lithography facilities are available, several regions of the specimen can be analyzed simultaneously for statistical sampling. 

Structural information as well as subterranean structures of solids. The surface-related properties of materials can therefore be better understood [46], There are several other advantages of surface investigation by HRTEM. For example, specimen preparation is simple. Normally, small particles with any size and any morphology can be directly used. Multiple scattering can normally be ignored, since the surface areas are often very thin and can legitimately be treated as weak phase objects, where the image intensity indicates the projected electrostatic potential. 

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